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Review Article

J. Med. Devices. 2019;13(2):020801-020801-6. doi:10.1115/1.4042794.

Developed countries struggle with high healthcare spending, and cost is often cited as a barrier to the introduction of new patient care technologies. The core objective of this review article is to help familiarize medical technology innovators with trends in the health economic environment and the implications for the adoption of new technologies. We review and discuss this topic in language accessible to medical technology innovators. We assess macrolevel developments in healthcare spending and highlight measures already taken to control spending. We discuss practical implications for anyone involved in healthcare innovation. Two observations are central to this discussion: (1) the U.S. spends significantly more on healthcare per capita than any other developed country; (2) across developed countries, healthcare spending has risen steadily over the past two decades. Nevertheless, higher spending has not always led to improvements in health. As a result, innovators need to be prepared to navigate an outcomes-oriented and value-based environment that is being defined by the emerging requirements of various healthcare stakeholders. Practically, new products should aim to improve health outcomes at a cost deemed “good value” and/or reduce cost for one or multiple stakeholders. Opportunities also exist for tools that enable cost/outcomes tracking, which will help demonstrate value to providers, insurers, and patients.

Commentary by Dr. Valentin Fuster

Research Papers

J. Med. Devices. 2019;13(2):021001-021001-9. doi:10.1115/1.4042599.

Many medical conditions, including sensory processing disorder (SPD), employ compression therapy as a form of treatment. SPD patients often wear weighted or elastic vests to produce compression on the body, which have been shown to have a calming effect on the wearer. Recent advances in compression garment technology incorporate active materials to produce dynamic, low bulk compression garments that can be remotely controlled. In this study, an active compression vest using shape memory alloy (SMA) spring actuators was developed to produce up to 52.5 mmHg compression on a child's torso for SPD applications. The vest prototype incorporated 16 SMA spring actuators (1.25 mm diameter, spring index = 3) that constrict when heated, producing large forces and displacements that can be controlled via an applied current. When power was applied (up to 43.8 W), the prototype vest generated increasing magnitudes of pressure (up to 37.6 mmHg, spatially averaged across the front of the torso) on a representative child-sized form. The average pressure generated was measured up to 71.6% of the modeled pressure, and spatial pressure nonuniformities were observed that can be traced to specific garment architectural features. Although there is no consistent standard in magnitude or distribution of applied force in compression therapy garments, it is clear from comparative benchmarks that the compression produced by this garment exceeds the demands of the target application. This study demonstrates the viability of SMA-based compression garments as an enabling technology for enhancing SPD (and other compression-based) treatment.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021002-021002-10. doi:10.1115/1.4043016.

We present novel medical devices for safe surgical puncturing, in particular a cannula for the treatment of retinal vein occlusion (RVO). This passive mechanical device has an adjustable stroke and exerts a puncturing force independent of operator applied displacement. The innovative feature of this tool is that puncturing stroke is decoupled from operator input thereby minimizing the possibility of overpuncturing. This is achieved using our concept of stability programming, where the user modifies the mechanism strain energy as opposed to imposing direct displacement which is the case for standard bistable mechanisms. Ultra-fast laser three-dimensional (3D) printing is used to manufacture the needle in glass. A microfluidic channel is integrated into the needle tip for drug injection. Numerical simulations and experimental measurements validate the mechanical stability behavior of the puncture mechanism and characterize its puncturing stroke and force.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021003-021003-9. doi:10.1115/1.4043018.

Slip, or accidental loss, of grasped biological tissue can have negative consequences in all types of surgery (open, laparoscopic, robot-assisted). This work focuses on slip in robot-assisted surgery (RAS) with the goal of improving the quality of grasping and tool–tissue interactions. We report on a survey of 112 RAS surgeons, the results of which support the value of detecting and reducing slip in a variety of procedures. We conducted validation tests using a thermal slip sensor in a surgical grasper on tissue in vivo and ex vivo. The results of the survey and validation informed a user study to assess whether tissue slip feedback can improve performance and reduce effort in a phantom tissue manipulation task. With slip feedback, experienced subjects were significantly faster to complete the task, dropped tissue less (3% versus 38%), and experienced decreased mental demands and situational stress. These results provide motivation to further develop the sensor technology and incorporate it in robotic surgical equipment.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021004-021004-8. doi:10.1115/1.4043078.

Hemolysis is a challenging problem and still represents a frequent source of errors in blood test laboratory practice. Due to the broad and heterogeneous bias induced in the measurement of several parameters by hemolysis, inaccurate results may be reported, and the patient may be required to repeat sample collection, delaying diagnosis. Existing automated laboratory devices including hemolysis detection are not suitable for lower volume and smaller sample collection sites. In many situations, hemolysis is still detected by visual inspection of the sample after centrifugation, during the blood test pre-analytical stage. Visual inspection is highly dependent on a qualified workforce, subjective to interpretation discrepancies, and thus difficult to standardize. The paper aims to describe the design and performance of a portable device for measuring hemolyzed samples based on computer vision and neural network. The results indicate that the device provides hemolysis indexes with sufficient accuracy to guide laboratory decision in the blood test pre-analytical stage.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021005-021005-6. doi:10.1115/1.4043109.

Bone deformities are often complex three-dimensional (3D) deformities, and correcting them is difficult. To correct persistent clubfoot deformity in adolescents or adults, an external fixator is sometimes used to encourage tissue growth and preserve healthy tissues. However, it is difficult to set up, resulting in long surgeries and steep learning curves for surgeons. It is also bulky and obstructs patient mobility. In this paper, we introduce a new approach of defining clubfoot deformity correction as a six degrees-of-freedom (6DOF) correction, and then reducing it to just two degrees-of-freedom (2DOF) using the axis-angle representation. Therefore, only two physical trajectory joints are needed, which in turn enables a more compact fixator design. A computer planner was developed to minimize the bulk of the external fixator, and to optimize the distraction schedule to avoid overstretching the soft tissues. This reduces the learning curve for surgeons and shortens surgery time. To validate the system, a patient-specific clubfoot simulator was developed, and four experiments were performed on the clubfoot simulator. The accuracy of midfoot correction was 11 mm and 3.5 deg without loading, and 41 mm and 11.7 deg with loading. While the external fixator has to be more rigid to overcome resistance against correction, the surgical system itself was able to achieve accurate correction in less than 2 h. This is an improvement from the current method, which takes 2.5–4.5 h.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021006-021006-9. doi:10.1115/1.4043017.

Trans-oral laser microsurgery (TLM) is a surgical procedure for removing malignancies (e.g., cysts, polyps, tumors) of the laryngeal region through laser ablation. Intraoperative microsurgical forceps (i.e., microforceps) are used for tissue manipulation. The microforceps are rigid, single degree-of-freedom (DOF) devices (open–close) with precurved jaws to access different parts of the curved cylindrical laryngeal region. These microforceps are manually handled and are subject to hand tremors, poor reachability, and nonergonomic use, resulting in poor efficacy and efficiency in the surgery. A novel 3DOF motorized microforceps device is presented here, integrated with a 6DOF serial robotic manipulator. The device, referred to as RMF-3, offers three motorized DOFs: (i) open–close forceps jaw; (ii) tool rotation; and (iii) tool-tip articulation. It is designed to be compliant with TLM spatial constraints. The manual handling is replaced by tele-operation device, the omega.7. The design of the RMF-3 is characterized through theoretical and experimental analysis. The device shows a maximum articulation of 38 deg and tool rotation of 100 deg. Its performance is further evaluated through user trials using the ring-in-loop setup. The user trials demonstrate benefits of the 3DOF workspace of the device along with its teleoperation control. RMF-3 offers an improved workspace and reachability within the laryngeal region. Surgeons, in their preliminary evaluation of the device, appreciated the ability to articulate the tip, along with rotation, for hard-to-reach parts of the surgical site. RMF-3 offers an ergonomic robotic teleoperation control interface which overcomes hand tremors and extreme wrist excursion which leads to surgeon pain and discomfort.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021007-021007-8. doi:10.1115/1.4043196.

In medical jet injection, a narrow fluid drug stream is propelled at high velocity into skin without a needle. Previous studies have shown that the volume delivered is highly dependent on a number of factors. This paper details the development of an electronic force sensor for medical jet injection and shows that the normal contact force exerted on the tissue by the nozzle is an additional factor affecting volume delivered. Using this sensor, we measure the forces at the nozzle tip in the normal direction with a sensitivity of 18 μN, calibrated over a range from 1 N to 8 N with a mean absolute error of 8 mN, and a maximum overload of 300 N. We further measure forces at the nozzle tip in the lateral direction with a sensitivity of 8 μN, calibrated over a range from 0.1 N to 7 N, with a mean absolute error of 101 mN for lateral contact force magnitude and 1.60 deg for lateral contact force direction. Experimental validation confirms that the force sensor does not adversely affect the accuracy and precision of ejected volume from the jet injector. We use this setup to examine the effect of normal contact force on volume delivered into postmortem porcine tissue. Experimental results demonstrate that volume delivered with normal contact force between 4 N and 8 N is significantly more accurate and precise compared to volume delivered with normal contact force between 0 N and 3.9 N.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021008-021008-9. doi:10.1115/1.4043292.

Stent grafts are medical devices used to treat abdominal aortic aneurysms (AAAs) in endovascular aneurysm repair (EVAR). Computational and experimental models have been developed to study stent graft delivery and deployment during EVAR; however, frictional properties have not been taken into account in most previous studies. The objective of this study was to determine the coefficients of friction of three commercially available stent grafts (Cook Zenith, Medtronic Endurant, and Vascutek Anaconda), their delivery sheaths, a porcine aorta, and two mock arterial materials. Stent grafts were obtained and separated into stents, graft fabric, and sheaths. Using a custom-made friction measurement apparatus, the coefficients of friction were measured between five material pairs: (i) the stents and inner surface of the sheath, (ii) the graft fabric and inner surface of the sheath, (iii) the outer surface of the sheath and a porcine aorta, (iv) the outer surface of the sheath and three different polyvinyl alcohol (PVA) cryogels, and (v) the outer surface of the sheath and a polydimethylsiloxane (PDMS) sheet. The results show that the coefficients of friction between the graft fabric and the sheath were higher than those between the stents and the sheath. The PVA cryogels showed more comparable frictional properties to the porcine aorta than did the PDMS sheet, suggesting that PVA cryogels provide a more accurate approximation for the in vivo frictional properties. These results can be used to improve the accuracy of computational models for stent graft delivery and deployment and to select appropriate materials for vascular phantoms.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021009-021009-10. doi:10.1115/1.4043052.

Patients treated by current ventricular assist devices (VADs) suffer from various post implantation complications including gastrointestinal bleeding and arteriovenous malformation. These issues are related to intrinsically mismatch of generated flow by VADs and the physiological flow. In addition, the common primary drawback of available VADs is excessive surgical dissection during implantation, which limits these devices to less morbid patients. We investigated an alternative soft VAD (SVAD) system that generates physiological flow, and designed to be implanted using minimally invasive surgery by leveraging soft materials. A soft VAD (which is an application of intraventricular balloon pump) is developed by utilizing a polyurethane balloon, which generates pulsatile flow by displacing volume within the left ventricle during its inflation and deflation phases. Our results show that the SVAD system generates an average ejection fraction of 50.18 ± 1.52% (n = 6 ± SD) in explanted porcine hearts. Since the SVAD is implanted via the apex of the heart, only a minithoracotomy should be required for implantation. Our results suggest that the SVAD system has the performance characteristics that could potentially make it useful for patients in acute and/or chronic heart failure, thus serving as a bridge-to-transplantation or bridge-to-recovery.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021010-021010-11. doi:10.1115/1.4043293.

Mechanical loosening of implants is in the majority accompanied with a periprosthetic interface membrane, which has to be removed during revision surgery. The same is true if a minimal invasive (percutaneous) refixation of a loose implant is done. We describe the requirements for a waterjet applicator for interface tissue removal for this percutaneous hip refixation technique. The technical requirements were either obtained from a literature review, a theoretical analysis, or by experimental setup. Based on the requirements, a waterjet applicator is designed which is basically a flexible tube (outer diameter 3 mm) with two channels. One channel for the water supply (diameter 0.9 mm) and one for suction to evacuate water and morcellated interface tissue from the periprosthetic cavity. The applicator has a rigid tip (length 6 mm), which directs the water flow to create two waterjets (diameter 0.2 mm), both focused into the suction channel. The functionality of this new applicator is demonstrated by testing a prototype of the applicator tip in an in vitro experimental setup. This testing has shown that the designed applicator for interface tissue removal will eliminate the risk of water pressure buildup; the ejected water was immediately evacuated from the periprosthetic cavity. Blocking of the suction opening was prevented because the jets cut through interface tissue that gets in front of the suction channel. Although further development of the water applicator is necessary, the presented design of the applicator is suitable for interface tissue removal in a minimally invasive hip refixation procedure.

Commentary by Dr. Valentin Fuster
J. Med. Devices. 2019;13(2):021011-021011-8. doi:10.1115/1.4043588.

Oximeter is an important clinical device used for measuring peripheral capillary oxygen saturation (SpO2) in blood and hence accurate results are needed in order to help physicians predict clinical problems in the initial stage(s) of liver or kidney diagnosis. Different issues associated with the accuracy of SpO2 and heart rate measurement accuracy are studied in this work. With the understanding of these issues, a new SpO2 monitoring system is proposed that comprises of a better detection method, novel discrete time signal processing (DTSP) algorithm, and a custom-made oximeter probe head. The proposed SpO2 measurement system is capable of determining low levels of SpO2 present in human blood and produce the results in a short time that enable real-time monitoring of a patient SpO2. It can also distinguish low level of SpO2 against background noise.

Commentary by Dr. Valentin Fuster

Technology Review

J. Med. Devices. 2019;13(2):024001-024001-10. doi:10.1115/1.4042795.

The aims of this study were (1) to identify research publications studying noninvasive electrocardiogram (ECG) monitoring devices, (2) to define and categorize current technology in noninvasive ECG recording, and (3) to discuss desirable noninvasive recording features for personalized syncope evaluation to guide technological advancement and future studies. We performed a systematic review of the literature that assessed noninvasive ECG-monitoring devices, regardless of the reason for monitoring. We performed an Internet search and corresponded with syncope experts and companies to help identify further eligible products. We extracted information about included studies and device features. We found 173 relevant papers. The main reasons for ECG monitoring were atrial fibrillation (n = 45), coronary artery disease (n = 10), syncope (n = 8), palpitations (n = 8), other cardiac diseases (n = 67), and technological aspects of monitoring (n = 35). We identified 198 devices: 5 hospital telemetry devices, 12 patches, 46 event recorders, 70 Holter monitors, 23 external loop recorders, 20 mobile cardiac outpatient telemetries, and 22 multifunctional devices. The features of each device were very heterogeneous. There are a large number of ECG-monitoring devices with different features available in the market. Our findings may help clinicians select the appropriate device for their patients. Since there are only a few published articles analyzing their usefulness in syncope patients, further research might improve their use in this clinical setting.

Commentary by Dr. Valentin Fuster

Technical Brief

J. Med. Devices. 2019;13(2):024501-024501-6. doi:10.1115/1.4042866.

This paper describes a novel percutaneous ultrasound gastrostomy (PUG) procedure and the CoapTech point-of-care ultrasound magnet-aligned gastrostomy (PUMA-G) device, which were developed to allow the placement of gastrostomy tubes by physicians across a variety of specialties, using ultrasound equipment found in many nonspecialized medical locations while consuming fewer resources. The current practice for the placement of gastrostomy tubes requires highly specialized equipment and trained physicians, which can delay the performance of the procedure or make it inaccessible in some locations. The PUMA-G device consists of an orogastric catheter with a balloon that encloses a magnetic bar at its distal end and an external, handheld magnet. The orogastric tube is passed through the mouth or the nose and into the stomach. The external magnet is then used to maneuver the balloon to the desired location in the stomach, with feedback and guidance from real-time ultrasound visualization. The novelty of this approach is the use of magnets to create the static compressive force needed for coaptation, in which the stomach is pushed flush against the abdominal wall, allowing ultrasound visualization of the entire gastrostomy tract (skin to stomach), safe cutaneous puncture, and guidewire-assisted placement of the gastrostomy tube. The development of the PUMA-G device has been aided by benchtop and simulation testing in addition to canine and human cadaver studies. The PUMA-G device was used successfully in 29 of 30 cadaver tests, with the one failure attributed to operator error and not the device. Further testing in live patients will assess the safety of the procedure, the speed with which it can be completed, the cost savings, and other benefits the device might offer over the existing gastrostomy procedures.

Commentary by Dr. Valentin Fuster

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